[Artlav]

Layers of patterns.

The whole point of programming is to take something complex and break it down into simple arithmetics and logic that a computer can digest.

So you build simple, isolated expressions that do one slightly more complex thing using slightly less complex things, then use these expressions to build slightly more complex things, and so on recursively, all the way up to having a "do the thing" button in an app.

Having these isolated, modular, layers of testable implementations is what makes code that can survive the test of time.

[cimmanom]

Yup. Combined with this, the "single level of abstraction" principle can make for much more readable and maintainable code.